1. Field of the Invention
The present invention relates to an external treatment agent such as a cosmetic containing fine soft microcapsules. More specifically, it relates to an external treatment agent containing gelatin capsules enclosing a liquid and/or solid hydrophobic component or a water-in-oil type emulsion therein, in which the capsules are not broken during the preparation of external treatment agents such as cosmetics, drugs, quasi drugs, but can be broken easily without escape on the palms of the hands upon usage (i.e., the term "escape" refers to the stage wherein the capsules are rubbed through the fingers or palms without rupture when the fingers and palms of the hands are rubbed together, to uniformly mix the aqueous phase which is the base and the capsules with the fingers or palms), whereby the contents are leaked out to be mixed with the outer phase, and there is no feeling of foreign matter caused by portions of the capsule films remaining after breaking, which external treatment agents also have a good useability and excellent luster imparting effect and skin wettability, or in which the unstable water-soluble substance and lipid-soluble substance enclosed within the capsules exhibit an excellent stability without deterioration for a long term, and have an excellent luster imparting effect and wettability of the skin, with a good useability.
The present invention further relates to a method for producing microcapsules by microencapsulating hydrophobic substances according to a complex co-acervation and a simple co-acervation by using a hydrophilic polymer, which comprises previously forming a co-acervate and then successively adding hydrophobic substances with different properties, whereby microcapsules enclosing separate hydrophobic substances can be obtained at the same time in one step without a mutually mixing of the hydrophobic substances during production, which is extremely cost-advantageous.
2. Description of the Related Art
Generally speaking, so-called external treatment agents include cosmetics, drugs, and quasi drugs. Among the above, the cosmetics are classified into basic make-up cosmetics and hair cosmetics, depending on the location at which they act or their purpose.
The basic cosmetics include cosmetic water, emulsion, and cream, which are used for applying oily components having a good quality or a hydrophilic substance having a high humectant property with a good balance to the skin when the balance of the skin humectant mechanism in a human body is disturbed by various external conditions (wind, temperature, humidity, etc.) or inherent conditions (age, etc.). For example, a cosmetic water emulsion is a hydrophilic cosmetic having a transparent appearance, comprising a humectant component, an alcohol, and water, etc., and the emulsion and cream are cosmetics comprising an oily component and an aqueous component mixed in a suitable ratio.
As make-up cosmetics, a foundation, eyeshadow, and lipsticks, may be included. These are used for varying the skin color by the application of a color, affording a three-dimensional feeling to the skin, to emphasize the color of a part of or conceal a defect of the skin, thereby creating an attractive appearance while simultaneously conditioning the skin.
The hair cosmetics include hair tonics, hair oils, and hair creams, which are used as hair conditioners and as a nutrient for the hair.
More specifically, the common function or purpose of these cosmetics is to maintain a healthy and normal stage (homeostasis) by applying a suitable oily component and humectant component or water, in accordance with the nature of the skin or hair, to thereby assist the natural humectant mechanism of skin or hair and alleviate deterioration of the skin or hair caused by changes in external environmental conditions, including natural conditions such as temperature and humidity and artificial conditions such as defatting by washing.
For an improvement of these functions, various skin effective components such as vitamins and unsaturated fatty acids have been added in the prior art emulsion type cosmetics. As effective components, although water-soluble substances such as vitamin C, etc. and lipid-soluble substances such as vitamin A, linolenic acid, etc., are known, most of the water-soluble effective components are hydrolyzed when placed in contact with water, and thus the physiological activities thereof are lost. On the other hand, most of the lipid-soluble effective components are very susceptible to auto oxidation and, after forming activated radicals through a loss of hydrogen atoms by light or heat, form peroxy radicals by an absorption of oxygen, and are decomposed or polymerized via hydroperoxide (peroxide) to thereby forming carbonyl compounds, lower aldehydes, lower fatty acids, ketones and other polymers, and thus the activities thereof are lost.
Accordingly, when formulating these effective components in cosmetics or other external agents, oxidation must be prevented. As one means of preventing oxidation, a method in which the preparation of an external agent is preformed in an inert gas atmosphere such as nitrogen, and further, during filling of the product in a vessel, the air in the space in contact with the external agent is replaced with nitrogen or carbon dioxide, can be used. But this replacement with nitrogen has little effect unless not only the oxygen in the space portion but also the dissolved oxygen in the external agent are replaced with nitrogen, and the replacement with carbon dioxide may cause an undesirable rise in the acid value of the effective components, or an objectionable odor, with a lapse of time. Such preparation and storage can be performed at as low a temperature as possible, but this is practically almost impossible if the quality is to be guaranteed. Accordingly, a stabilization of external agents, for a long term has been effected by an addition of antioxidants, but since the properties and the effective concentration of antioxidants differ in accordance with the kind of effective skin component used, a drawback has arisen in that a thorough examination and much experimentation are required before practical use, which makes the method difficult to handle.
Also, the method of enclosing water-soluble and lipid-soluble effective components within microcapsules, to separate them from water and oxygen, has been investigated. But, in the known methods, a simultaneous microcapsulation of water-soluble and lipid-soluble components has been considered impossible, and the method in which the respective components are prepared separately by microcapsulation methods entirely different from each other and thereafter mixed has been used, and therefore, the preparation must be performed at least twice, which greatly increases labor costs. Further, when microcapsules enclosing a water-soluble effective component therein are formulated in a base of a cosmetic water or cream, in which water is the medium, a problem has arisen in that the water readily passes through the inside and outside of a capsule film, whereby the contents leak into the outer phase base within a short time.
In the prior art, microcapsules comprising a gelatin wall film swollen with water and enclosing liquid oil components have been formulated as an external agent, but these required an extremely strong breaking force because of the flexible wall films and contents therein when they are to be broken by compression by rubbing the palms of the hand together upon usage. Namely, when palms of the hands were rubbed together, the microcapsules were only slid over the skin surface or embedded in the skin pores, whereby sometimes breaking did not occur, and thus the efficacy of the oil components enclosed was not exhibited.
For example, as mentioned above, a cosmetic water is prepared by solubilizing an oil component (i.e., emollient agent), a flavor, and a medicament, to obtain a transparent appearance, and an O/W type emulsion or cream is prepared as an emulsion containing a large amount of an emulsified oil component, thereby enhancing the humectant effect and the emollient effect on the skin. Namely, to enhance the emollient effect on the skin, a large amount of an oil component is formulated by solubilization or emulsification with a large amount of an emulsifier, but the emulsifiers generally used more or less irritate the skin, in spite of the surfactant ability thereof. Accordingly, from the viewpoint of safety, the amount of surfactant formulated therein is limited, and thus the amount of the oil component to be solubilized and emulsified must be limited. Namely, a problem has arisen in that the desired humectant effect or the emollient effect cannot be imparted to the skin.
As a means for solving these problems, the formulation of microcapsules enclosing an oil component in a cosmetic has been considered. For example, Japanese Unexamined Patent Publication (KOKAI) No. 61-112897 discloses a surfactant solution containing capsules having an improved dispersibility provided by an adjustment of the specific gravity. Also, Japanese Unexamined Patent Publication (KOKAI) No. 59-73510 disclosed that, by formulating capsules comprising a polymerizable polymeric film enclosing a skin emollient component, a flavor, and a drug component in a cosmetic, the feeling during use of a make-up cosmetic can be improved. But, according to trace experiments by the present inventors, "escape" of the capsules disclosed by the former specification occurred during usage, and thus the capsules cannot be easily disintegrated by compression, whereby a leakage of the enclosed contents could not be realized. On the other hand, the capsules used in the latter specification, when formulated in a cosmetic water or cream, can be disintegrated by compression only with difficulty, due to extremely fine capsule particle sizes of 1 to 100 .mu.m, and further, even if integrated the film substance of the capsules remained, thus having the drawback of a feeling of foreign matter on the skin.
Furthermore, it is known to control the strength of the wall film by controlling the thickness of the wall film of a microcapsule or formulating a fine powder of mica and titanium into the wall film. But, in the former method of controlling the film thickness, the film must be made extremely thin so that the capsules are easily broken, and therefore, the capsules may sometimes break during the preparation of the product. Further, when microcapsules are to be prepared by the co acervation method, in which a gelatin film is formed after dispersing the oil component into water, the particle sizes of the capsules are nonuniform, and the breaking strength differs in accordance with the particle size even if the film thickness is the same, and therefore, the breaking strength must be based on both the film thickness and the particle size, and thus the preparation becomes extremely complicated. On the other hand, in the latter method of using a fine powder, the transparency of the gelatin film is impaired, depending on the kind of fine powder used, and therefore, the film cannot be applied to a product in which the color of the content is emphasized. Further, when the above co acervation method is utilized, since a fine powder is added into the outer phase, the amount precipitated together with the coacervate on the oil droplet surface is extremely small, and most of it is discarded together with the outer aqueous phase in the washing step, which is cost-disadvantageous, and even if the fine powder is contained in the wall film, the differences in breaking strength due to the size of capsule still remain as a disadvantage thereof.
Many methods for micro encapsulating hydrophobic substances are known, and of these methods, the co acervation method utilizing the phase separation phenomenon of hydrophilic polymer can be practiced relatively easily if a device for emulsifying and dispersing hydrophobic substances into water is used, and finished microcapsules having dense wall films with a high coverage ratio can be produced, and thus this is an industrially useful production method.
In the prior art, when microcapsules are to be produced by the co acervation method, hydrophobic substances are dispersed or emulsified in an aqueous solution of a hydrophilic polymer to desired particle sizes, and then a hydrophilic polymer having opposite charges in the case of the complex co acervation method, or an electrolyte or a poor solvent are added in the case of the simple co acervation method, to effect microencapsulation.
Such prior art methods are useful for the microencapsulation of one kind of hydrophobic substance, but are not suitable for the microencapsulation of two or more kinds of hydrophobic substances with different properties. When microcapsules are produced by coacervation after dispersion or emulsification by successively adding hydrophobic substances into an aqueous hydrophilic polymer solution, an agglomeration or mutual coalescence of the hydrophobic substances will occur during dispersion or emulsification, and thus microcapsules of mixed hydrophobic substances are formed and microcapsules enclosing separate hydrophobic substances can not be obtained. Accordingly, when several kinds of microcapsules enclosing different hydrophobic substances are to be formulated in a product, the number of steps must correspond to the number of kinds of microcapsules, and must be repeated to produce microcapsules enclosing different hydrophobic components, and thereafter, the respective microcapsules must be uniformly mixed into the product.
Generally speaking, when producing microcapsules by coacervation, hydrophobic substances are enclosed with a water-soluble polymer, and thereafter the water-soluble polymer is hardened and made insoluble in water. Since a substance of higher reactivity such as aldehydes is used as the hardening agent, a washing operation must be carried out to completely remove excess hardening agent, e.g., by thoroughly washing the microcapsules after production with purified water. To accomplish this washing, a method in which the steps of removing the aqueous phase portion after complete separation of the microcapsules by standing and again adding the same amount of purified water are repeated, and a method in which the steps of adding the same amount of purified water after separation of the microcapsules from the aqueous phase with a filter are repeated, are known, but both require much time and labor.
Therefore, in the above method in which the same number of steps as the kinds of capsules are repeated, too much time and labor are required for preparing one product, which is extremely cost-disadvantageous.
Also, in the coacervation method, microcapsules with extremely different size or of wall films states may be formed if slight changes in conditions occur, and therefore, when formulating many kinds of microcapsules enclosing different hydrophobic substances in a product, conventionally the sizing was made with a sieve, or the uniformity was disregarded, but the cost was disadvantageously high and a product having a satisfactory appearance could not be obtained.